1. Field of the Invention
This invention relates to the deposition of material onto a substrate and, more particularly, to a method for texturing the surface of a substrate to enhance the adhesion and reduce the stress concentration of a deposit on the substrate surface and the method is useful to deposit metals onto substrates used as shields in PVD and CVD chambers.
2. Description of Related Art
The deposition of a material onto a substrate to provide a coated surface is important for a number of industrial processes including painting, metal plating of electronic components, protecting the substrate from corrosion and the like. There are a number of coating processes used in industry such as painting, electrolytic and electroless plating, chemical vapor deposition (CVD) and physical vapor deposition (PVD). Regardless of the deposition process however, it is important that the substrate surface to be coated has a surface texture or other surface properties so that the deposit will not peel from the surface and be tightly held to the surface.
It is generally preferred that the surface of the substrate to be coated has a texture which enhances the adhesion of the deposit. Various techniques have been used to provide a textured surface such as sand or grit blasting, chemical cleaning or treatment to etch the surface as with acid and other corrosive type materials, adhesives, etc. Once the surface has been textured, the desired deposition material may be applied to the surface by any conventional method including brushing, spraying, dipping, roll coating, electrostatic coating or deposition, immersion, and the like.
Unfortunately, many of the texturing processes are not commercially satisfactory and/or present environmental problems because of the use of dangerous materials requiring safe and environmental disposal after use. While the present invention will be applicable to prepare any surface for deposition of a coating on the surface thereof the following description will be directed to the making of coated shields used in CVD and PVD chambers.
In the fabrication of semiconductor devices, a frequently used technique involves deposition of a metallic layer on the surface of a wafer. A physical vapor deposition (PVD) apparatus as shown in U.S. Pat. No. 6,030,509 to Fu Kang et al. may be used to deposit metal films on wafer surfaces and the disclosure of this patent is hereby incorporated by reference. The PVD apparatus is generally termed a sputtering apparatus and a wafer is placed inside a vacuum chamber and positioned on a wafer holder. The wafer holder is normally supported on the bottom wall of the vacuum chamber by insulating means and the vacuum chamber is further equipped with a sputtering gas inlet which is connected to a gas supply such as argon or other inert gases. A gas outlet is also provided in the chamber and it is connected to an evacuation pump to maintain the desired pressure within the chamber during the metal deposition process.
A target of a suitable metallic material is mounted to the top wall of the chamber and is electrically connected to the negative terminal of a power supply. The chamber further includes a cylindrical chamber shield which typically has top extensions adjacent to the edges of the metal target and bottom extensions which overlap the bottom edge of the wafer holder. During the process the target is energized and metal particles are ejected from the target and coat the wafer. The wafer holder in combination with the chamber shield protects the lower chamber cavity of the PVD chamber from the metal particles ejected from the target during the deposition process. Such contamination of the lower chamber is undesirable since cleaning of the cavity requires a substantial downtime.
The shields can be removed for cleaning and reused and are typically made from stainless steel or aluminum. Stainless steel provides a more durable shield than aluminum.
The shield substrate typically has a deposit on the surface thereof to enhance the life of the shield and it is important that the deposition material on the shield substrate be tightly adhered thereto to reduce the shedding of particles of the deposit onto the wafer during the process. Reducing stress concentrations in the deposit also reduces shedding of particles during thermal history (thermal expansions and contractions) of the PVD or CVD process.
The common method to make the shields is to grit blast the shield substrate (roughen the surface for adhesion) and aluminum arc spraying. The aluminum arc spraying applies a surface with pronounced protrusions for the deposition material such as titanium, tantalum, copper, titanium nitride, aluminum, as well as various other metal films to cover and adhere to the shield substrate. During thermal changes, the underlying aluminum surface is ductile and allows the deposition material to contract or expand with minimal fracturing. Fracturing and poor adhesion are the main contributors to shedding particles. A textured surface that minimizes stress concentrations in the deposit but still allows good adhesion and thermal properties is ideal for reducing shielding particle shedding during the PVD or CVD process.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide a method for preparing a surface of a substrate for deposition of a material thereon, such as a substrate used for a shield in a PVD or CVD process to increase the adhesion and/or lower the stress concentration of materials deposited on the surface of the substrate.
It is another object of the present invention to provide a substrate which has been prepared for the deposition of a material thereon such as a substrate used to make a shield for use in a PVD or CVD process.
A further object of the present invention is to provide coated articles made using the method of the invention such as shields used in a PVD or CVD process.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.
Broadly stated the present invention provides a textured substrate surface for enhanced deposition of a metal or other material to the substrate. The textured surface is preferably uniform and/or a controlled shape (e.g., abutting spheres) to mechanically grip the deposition material and minimize stress build-up through thermal history. The invention also provides increased porosity for out-gassing without sacrificing adhesion to the substrate surface. Particulate generation is also minimized during the process.
The above and other objects, which will be apparent to one skilled in the art, are achieved in the present invention which relates in one aspect to a method for depositing a material on a substrate comprising the steps of:
providing a substrate for depositing a material on the surface thereof;
coating the surface of the substrate with first particles which are preferably spherical but can be any optimized controlled shape, to form a coated substrate having a first bonding textured surface corresponding to the shape of the first particles in an abutted and/or overlapping relationship;
coating the first bonding textured surface with second particles which are preferably spherical to form an adhesion layer, the second particles preferably being larger and/or having a higher melting point than the first particles;
heating the coated substrate to reflow the first particles forming a reflowed first bonding surface wherein the second particles preferably in substantially their original size and shape are embedded in the reflowed first bonding surface forming a second adhesive textured surface preferably corresponding to the shape of the second particles in an abutted and/or overlapping relationship; and
coating a deposition material on the second adhesive textured surface to form the desired coated product.
In another aspect of the invention a method is provided for depositing a material on a substrate comprising the steps of:
providing a substrate for depositing a material on the surface thereof;
coating the surface of the substrate with first particles which are preferably spherical but can be any optimized controlled shape, to form a coated substrate having a first bonding textured surface corresponding to the shape of the first particles in an abutted and/or overlapping relationship;
heating the coated substrates to reflow the first particles forming a reflowed first bonding surface;
coating the reflowed first bonding surface with second particles which are preferably spherical but can be any optimized controlled shape, to form an adhesion layer, the second particles preferably being larger and/or having a higher melting point than the first particles;
heating the coated substrate to reflow the reflowed first bonding surface wherein the second particles preferably in substantially their original size and shape are embedded therein forming a second adhesive textured surface preferably corresponding to the shape of the second particles in an abutted and/or overlapping relationship; and
coating a deposition material on the second adhesive textured surface to form the desired coated product.
In a further aspect of the invention, a method is provided for texturing the surface of a substrate to enhance the adhesion of a material to be deposited on the substrate comprising the steps of:
providing a substrate for depositing a material on the surface thereof;
coating the surface of the substrate with first particles which are preferably spherical but can be any optimized controlled shape, to form a coated substrate having a first bonding textured surface preferably corresponding to the shape of the first particles in an abutted and/or overlapping relationship;
coating the first bonding textured surface with second particles which are preferably spherical but can be any optimized controlled shape, to form an adhesion layer, the second particles preferably being larger and/or having a higher melting point than the first particles;
heating the coated substrate to reflow the first particles forming a reflowed first bonding surface wherein the second particles preferably in substantially their original size and shape are embedded in the reflowed first bonding surface forming a second adhesive textured surface preferably corresponding to the shape of the second particles in an abutted and/or overlapping relationship.
In a further aspect of the invention, a method is provided for texturing the surface of a substrate to enhance the adhesion of a material to be deposited on the substrate comprising the steps of:
providing a substrate for depositing a material on the surface thereof;
coating the surface of the substrate with first particles which are preferably spherical but can be any optimized controlled shape, to form a coated substrate having a first bonding textured surface corresponding to the shape of the first particles in an abutted and/or overlapping relationship;
heating the coated substrates to reflow the first particles forming a reflowed first bonding surface;
coating the reflowed first bonding surface with second particles which are preferably spherical but can be any optimized controlled shape, to form an adhesion layer, the second particles preferably being larger and/or having a higher melting point than the first particles;
heating the coated substrate to reflow the reflowed first bonding surface wherein the second particles preferably in substantially their original size and shape are embedded therein forming a second adhesive textured surface corresponding to the shapes of the second particles in an abutted and/or overlapping relationship.
In an additional aspect of the invention, an article made by the method of the invention is provided which has a textured surface suitable for depositing a material thereon with enhanced adhesive properties.
In a further aspect of the invention an article made by the method of the invention is provided which has a deposited material thereon and which article is suitable for use as a shield in a PVD or CVD apparatus and process.